In a typical semiconductor manufacturing process, an integrated circuit chip (IC) is initially cut from a wafer, such as a silicon wafer, and is mounted upon the die pad unit of a lead frame. The die pad unit is configured to received the IC and contains electrical leads that extend from the die pad unit to the external portion of the lead frame. A wire bonding operation is then performed on the IC to connect input and output terminals of the IC to the appropriate electrical leads of the lead frame. The IC is next environmentally sealed by use of a ceramic or an epoxy. Finally, the electrical leads that extend to the external portion of the lead frame are trimmed and prepared for connection to a printed circuit board so as to conduct electrical signals between the input and output terminals of the IC and the printed circuit board.
The wire bonding operation is an important step in the semiconductor manufacturing process. In particular, the wire bonding operation requires high precision due to the increasing miniaturization of ICs and the their associated lead frames. With reference to FIG. 6, a wire bonding operation is typically accomplished by placing a workpiece 2 on a heater block 1. As shown, the IC workpiece 2 includes pads 21 and electrical leads 22. A capillary 3 is then lowered to a bonding position on the workpiece and a wire bond is formed.
The operation of the capillary is two-fold. As shown in FIG. 7, the capillary is generally held in a home or initial position above the workpiece prior to the bonding operation. The distance between the home position of the capillary and the workpiece is divided into two sections. The first section is an acceleration/deceleration motion section in which the capillary is driven with an acceleration/deceleration motion. After the capillary has moved through this section, the capillary enters the second or lower section. The second section is also known as the search level since the capillary is moved more slowly through the second section as the capillary prepares to contact the workpiece.
As the capillary enters the second section (or search level), a touch algorithm is input to the drive unit of the capillary such that the capillary moves with a uniform motion until it contacts the workpiece at the bonding position. Once the capillary reaches the bonding position, the uniform motion provides a uniform pressure to the workpiece or the capillary wire bonds the workpiece.
Although a conventional wire bonding apparatus has a high level of precision, problems occur due to manufacturing tolerances of the die pad unit and the IC and also improper placement of the IC upon the die pad unit. With reference to FIG. 6, the pads 21 and electrical leads 22 of the IC workpiece are placed on a heater block 1. As can be seen, the upper surface of the heater block 1 is inclined such that the heights from the capillary to each of the bonding positions Pt1, Pt2, Lt1, and Lt2 have differing lengths.
A conventional wire bonding apparatus generally does not compensate for these differing heights. Instead, conventional systems typically use the same height for the acceleration/deceleration motion section for each bonding position on a workpiece. This use of the same length acceleration/deceleration motion section causes each of the bonding positions to have differing uniform motion sections (or search levels). For instance, in the wire bonding operation shown in FIG. 6, if a acceleration/deceleration motion section is chosen based on the bonding position designated by Pt1, and subsequently used for the remaining bonding positions, the uniform motion sections for the bonding positions designated by Pt2 and Lt2 will have shorter uniform motion sections. Further, the bonding position designated by Lt1 will have a longer uniform motion section.
These difference in the uniform motion sections (or search levels) can degrade the wire bonding operation. For instance, if the uniform motion section becomes very short such as in the case of Pt2 and Lt2, the inertia of the capillary due to the acceleration/deceleration motion may cause the capillary to contact the bonding position with an undesired force or possibly become embedded in the IC at the bonding position. On the other hand, in instances where the uniform motion section is increased as in the case of Lt1, the speed of the capillary may become too slow and thus provide an improper wire bond.